The present invention relates to a process for preparing N,N′-di(3′,5′-dimethylphenyl) perylenebis(dicarboximide) (=C.I. Pigment Red 149).
It is known to prepare colorants of the perylene-3,4,9,10-tetracarboxylic diimide series by reacting perylene-3,4,9,10-tetracarboxylic dianhydride with primary arylamines.
Pigment Red 149 has the following formula:

The O-semicondensate has the following formula:

DE-A 1 807 729 discloses the reaction of perylenetetracarboxylic acid or anhydride with 3,5-dichloroaniline in the presence of condensation-accelerating agents, such as zinc chloride, zinc acetate or hydrochloric acid, in solvent or diluent media such as quinoline, quinaldine, naphthalene or trichlorobenzene. The dye is isolated from the reaction mixture by filtration, if appropriate after dilution of the reaction mixture with inert solvents such as alcohols, formamide, dimethylformamide, toluene, chlorobenzene or nitrobenzene, and subsequent washing with organic solvents and water. To remove any traces of perylenetetracarboxylic acid, the dye is decocted with dilute aqueous sodium hydroxide solution. Subsequently, the dye is converted into a useful pigmentary crystal form by dissolving in concentrated sulfuric acid and precipitating by dilution with water.
DE-A 2 210 170 discloses a corresponding process wherein perylene-3,4,9,10-tetracarboxylic acid is reacted with 2,4,6-trimethylaniline.
However, the use of acidic condensing assistants means disadvantages such as corrosion problems and losses in relation to the costly, in some instances, amine components due to secondary reactions.
EP-A 0 198 369 discloses a process for preparing arylimides of perylene-3,4,9,10-tetracarboxylic acid wherein perylene-3,4,9,10-tetracarboxylic dianhydride (perylenebisanhydride) is reacted with a primary arylamine in the presence of a dialkylamine as catalyst. The reaction can take place in the presence of inert diluents, such as dimethylformamide, N-methylpyrrolidone, o-dichlorobenzene, nitrobenzene, quinoline or 2-ethylhexanol. Preferably, however, the reaction is carried out without further diluent in the relevant mixture of arylamine and dialkylamine. The reaction product can be removed, if appropriate after dilution with a low-boiling alcohol, by filtration. Preferably, however, the mixture of excess arylamine and dialkylamine and, if appropriate, the inert diluent is distillatively removed after quantitative conversion, so that the reaction product remains behind as a dry residue.
CN-A 1310203 discloses a process for preparing perylenetetracarboxylic diimide pigments wherein perylenebisanhydride and primary amine is reacted in aqueous solution at a pH of 3 to 5 in the presence of an organic carboxylic acid having 1 to 5 carbon atoms. The crude pigment is subsequently subjected to an aftertreatment (finishing). To this end, the crude pigment is ball milled in the presence of a grinding assistant such as sodium chloride, sodium sulfate and sodium carbonate, an organic solvent and 1% to 5% by weight, based on the weight of the crude pigment, of a perylenetetracarboxylic diimide derivative. Subsequently, a post-finishing treatment is carried out in an aqueous medium in the presence of a surfactant.
In the examples, perylenebisanhydride is dissolved in 10% KOH solution, and 3,5-dimethylaniline and acetic acid are added to the solution. The reaction product is filtered off and washed neutral with water. The dried crude pigment is subsequently ball milled with sodium chloride, a small amount of N,N′-di-n-butylperylenebis(dicarboximide) and a xylene-ethyl acetate mixture. The mixture is finally transferred into a 2% by weight aqueous hydrochloric acid comprising 1% of a surfactant mixture, boiled, the pigment is filtered off, washed neutral with water, dried and comminuted.
One disadvantage with the process described in CN-A 1310203 is that the perylenebisanhydride has to be initially completely dissolved in aqueous potassium hydroxide solution and subsequently reprecipitated in finely divided form with acetic acid. This consumes appreciable amounts of acetic acid, which cannot be recovered. Moreover, some of the costly 3,5-dimethylaniline is lost by acylation. The dye obtained does not meet quality requirements and has to be inconveniently aftertreated in several finishing operations.
It is an object of the present invention to provide a simple process for preparing Pigment Red 149 without the disadvantages described above.